[Rockhounds] Fun with Sodium Carbonate...

[gene at fossilnut.com]

I'll second that for sodium carbonate. It tends to want to form more seed 
crystals, rather than deposit on existing seeds. As I recall it's a function 
of how much supersaturation the particular material will allow.  Carbonate 
alllows very little.

On the opposite end of this one is sodium thiosulfate, where you can take 
the decahydrate crystals and heat them to dissolve the material in its own 
water of hydration, cool it, and still have a solution. Then add one speck 
of thiosulfate and the whole thing instantly solidifies.

One method to address that is to cycle the temperture slowly up and down. 
What happens is that raising the temperature dissolves that smallest 
crystals faster than the bigger ones because they have the greatest surface 
to volume ratio. In effect you "digest' the smaller seed crystals and 
redeposit on the ones that remain during the cooling. This process needs to 
be controlled and is lots slower than growing easy to grow crystals, but it 
is used (in effect) in commercial crystallizers to grow crystals to the size 
needed to effectively filter them.

Gene Hartstein


----- Original Message ----- 
From: <pmodreski at aol.com>
To: <bj9709 at yahoo.com>; <rockhounds at lists.drizzle.com>
Sent: Monday, June 30, 2008 3:47 PM
Subject: Re: [Rockhounds] Fun with Sodium Carbonate...


> Hi Brett,
>
> Some chemicals/minerals readily form large crystals, and some just 
> don't--they are prone to just crystallize as fine-grained powders when 
> their solutions are dried or evaporated.? Sodium carbonate, I think, as 
> well as sodium bicarbonate, are two of the latter--I believe they are just 
> hard to produce as large (or even, readily visible) crystals.? So yes, I 
> suspect one readily gets massive stalactites from sodium carbonate, but 
> not much in the way of crystals.
>
> P.S., as you probably know, sodium bicarbonate occurs naturally, though 
> rarely, as the mineral nahcolite.? A more common mineral is trona, which 
> is a mixed sodium carbonate-bicarbonate hydrate.? Sodium carbonate 
> decahydrate is the mineral, natron, but it is also not very common.
>
> Pete
>
>
>
>
>
>
> -----Original Message-----
> From: Brett Allen Johnson <bj9709 at yahoo.com>
> To: rockhounds at lists.drizzle.com
> Sent: Mon, 30 Jun 2008 1:02 pm
> Subject: [Rockhounds] Fun with Sodium Carbonate...
>
>
>
> I am trying to build a nice collection of all the Carbonates. I have 
> started my
> collection with both the massive form (calcite travertine, smithsonite 
> nodules,
> rhodochrosite stalactite, etc) and large individual crystals 
> (rhodochrosite
> cubes, calcite points, siderite blades, etc).
> Recently, I found NaCo3 at the hardware store (pool PH thingy). It comes 
> in a
> powdery form and it easily dissolved in water.
> One of the crystal growing website says, "...to make a stalactite." by 
> using a
> solution of water / NaCO3 and wool string. That is fine and dandy for a 
> massive
> form of the crystallized NaCO3, but I would like to large crystals of 
> NaCO3,
> too.
> Any Suggestion???
>
>
>
>
>
>
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